1. Field of the Invention
The present invention relates to the field of power system and control method thereof, and in particular to a pulse width modulation (PWM) power system and control method thereof.
2. The Related Arts
The known DC-DC power supply structure comprises a constant-voltage output PWM power system able to output a voltage with constant amplitude. In such a system, when the load increases, the constant-voltage output PWM power system can adjust the PWM output so that the amplitude of the DC output current increases as the load increases.
FIG. 4 is a schematic view showing the structure of a known constant-voltage output PWM power system 400.
As shown in FIG. 4, the known PWM power system 400 comprises a PWM power source 410, a voltage detection unit 430 and a feedback signal generation unit 450. The PWM power source 410 receives DC input, such as, DC input voltage with 12V amplitude, from external current source through DC input terminal IN, performs PWM on the received DC input and supplies the PWM output (DC output) through DC output terminal OUT to a device expecting power supply. The voltage detection unit 430 detects the voltage amplitude Vout of the PWM output. The feedback signal generation unit 450 generates a feedback signal based on the voltage amplitude Vout detected by the voltage detection unit 430, and supplies the generated feedback signal to the feedback signal input terminal FB of the PWM power source 410. The PWM power source 410 maintains the voltage amplitude of the PWM output based on the feedback signal received by the feedback signal input terminal FB, such as, maintaining the voltage amplitude Vout as 17V for the PWM output, and amplifies the current amplitude Iout of the PWM output.
In known technique, the problem of the constant-voltage output PWM power system is that when the current amplitude of the PWM output increases, the efficiency and stability of the constant-voltage output PWM power system may be affected. For example, when the load connected to the constant-voltage output PWM power system increases, and the voltage amplitude Vout of the PWM output from the constant-voltage output PWM power system remains the same, the current amplitude Iout of the PWM output will greatly increase so that the circuit loss of the constant-voltage output PWM power system will greatly increase, and the temperatures of the components of the constant-voltage output PWM power system, such as, IC chips, and the load or supplied devices may also increase, more power is consumed and efficiency is lowered. As a result, the stability of the loop formed by the constant-voltage output PWM power system and the load or supplied device becomes poor.